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Napa Valley Groundwater Sustainability: A Basin Analysis Report for the Napa Valley Subbasin (Draft Chapters 6 and 7)

By Vicki Kretsinger Grabert, Reid Bryson, Ben Brezing

September 22, 2016 Watershed Information & Conservation Council

Overview

• Basin Analysis Report Contents

• Overview of Groundwater Conditions

• Groundwater/Surface Water Interaction

• Ch. 6 (Draft): Sustainable Yield Analysis

• Ch. 7 (Draft): Napa Valley Subbasin Sustainability Goal

• Next Steps

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SGMA Basin Analysis Report • What it is:

– Alternative submittal (functionally equivalent) to a Groundwater Sustainability Plan

– Basins that have been operated sustainably for at least 10 years

– Covers the whole DWR-designated basin

– Conditions typical throughout the basin

• What it is not: – Not the whole County

– Not the hillsides, MST, or Carneros areas

– Does not require return to pre-development conditions

– Does not focus on very local groundwater problems (like well interference)

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Basin Analysis Report Contents 1. Introduction 2. Physical Setting and Hydrogeology 3. Monitoring Network and Program 4. Groundwater Conditions

a) Groundwater b) Surface water

5. Historical, Current and Projected Water Supply and Demand

6. Sustainable Yield Analysis 7. Napa Valley Subbasin Sustainability Goal 8. Monitoring Network Evaluation and Reporting 9. Sustainable Groundwater Management 10. Summary Appendices

Comparison Table: GSP to Basin Analysis Report 4

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Groundwater

Basins • Napa Sonoma Valley Basin

• Napa Valley Subbasin • Napa-Sonoma

Lowlands Subbasin

• Berryessa Valley Basin

• Pope Valley Basin

• Suisun-Fairfield Valley Basin

SGMA Medium Priority; applies to this Basin

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GW Level Monitoring, 2015

Napa Co., 100 (incld. 48 volun., 10 SW/GW)

DWR, 4 GeoTracker, 9

Total Wells = 113 Sites

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0

10

20

30

40

50

60

1950 1960 1970 1980 1990 2000 2010

Pre

cip

itatio

n (

in.)

Napa Precipitation

-40

0

40

80

120

160

200

Gro

undw

ate

r E

levatio

n

(ft.

, m

sl)

St. Helena

Yountville

Napa

Groundwater Conditions: Napa Valley Subbasin

Dry Years

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Depth to

Groundwater

Feet below ground surface

10 to 20 ft

Water table (Valley Floor) generally very shallow; basin quite “full” Spring 2015 8 Spring 2015

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Groundwater/Surface Water Interaction

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Groundwater Interactions with Surface Water

• Perennial Streams Recharge the Napa Valley Subbasin

• Groundwater contributes to stream baseflow

USGS Napa River near Napa

USGS Napa River near St Helena

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Historical to Current Streamflow Observations

• Historical streamflows in Napa Valley varied

considerably season-to-season & year-to-year

(USGS WRI 13-73, 1973)

1930s 1960s 1970s 2012-2015

SUMMER FALL 11

Day

s

Napa River near Napa: Days with no Flow

Total Baseflow (GW) & Stormflow

Historical variations in amount of annual baseflow.

Napa River near Napa

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0

50,000

100,000

150,000

200,000

250,000

300,000

350,000

400,000

450,000

500,000

19

30

19

32

19

61

19

63

19

65

19

67

19

69

19

71

19

73

19

75

19

77

19

79

19

81

19

83

19

85

19

87

19

89

19

91

19

93

19

95

19

97

19

99

20

01

20

03

20

05

20

07

20

09

20

11

20

13

20

15

Acr

e-F

eet

/ W

ate

r Ye

ar

Water Year

Total Stormwater Discharge

Total Baseflow Discharge

Base Period 1988 to Present

Data Missing

Very Wet Water Year (2006)

Very Dry Water Year (2007)

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Average Napa River Baseflow

Baseflow estimate is from stream gage data.

Historical seasonal variations in flow are typical. 13

(Napa River near Napa)

Dry Year

Monitoring at 5 Sites • Shallow MWs each

site

– Levels & quality

• Stream gauge each site

– Streamflow & quality

Surface Water/ Groundwater

5

4

3 2

1 14

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GW Monitoring Wells Near River

Above

Ground Locked

Protection

Below Ground “Nested”

Monitoring Wells

Looking Down

at MWs

2-inch dia.

casings

2-inch dia.

casings

Sand

and

Gravel

Sand Not to Scale 100 ft Deep

40 ft Deep

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SW/GW Interaction: Site 5: St. Helena, Oct. 2014 & Dec. 2014

S D 206.08ft

December

185.85ft

GW below in Oct. 2014 Not drawn to scale

October

173.05ft

189.04ft

40ft TD

100ftTD

WL Elev., msl

Elevation of Thalweg

196.00ft, msl

GW above in Dec. 2014

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SW/GW Interaction: Site 5 St. Helena

WL Difference Shallow and Deep Oct. 2015 = 17 ft.

River

Deep MW

Shallow MW

Streambed

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Groundwater/Surface Water Summary

• Overall, groundwater conditions stable

• Shallow depth to groundwater in the Valley Floor; the basin is quite “full”

• Historical streamflows varied considerably season-to-season and year-to-year

• Groundwater contributes to the total volume of streamflow

• Napa River system is hydrogeologically sensitive to climatic variations and other factors that change the water balance

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Chapter 6: Sustainable Yield Analysis

• Hydrologic Base Period Determination

• Water Budget

• Groundwater Level Change in Storage

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Hydrologic Base Period “Sustainable yield means the maximum quantity of water, calculated over a base period representative of long-term conditions in the basin and including any temporary surplus, that can be withdrawn annually from a groundwater supply without causing an undesirable result.” (Section 10721(v))

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Water Budget

• Subbasin conceptual model

• Compile available data to calculate Subbasin inflows and outflows

• Evaluate average change in Subbasin storage based on Subbasin inflows and outflows

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Water Budget: Core Element of Groundwater Sustainability Inflows – Outflows = S Change in GW Storage

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Upland Subsurface

Inflow Groundwater Recharge

Upland Runoff Surface Water

Deliveries

Urban Wastewater

Outflow

Groundwater

Pumping

Surface Water Outflow

Baseflow

Groundwater Storage

(saturated aquifer pore space)

Subsurface Groundwater Outflow (to Napa-Suisun

Lowlands Subbasin)

Changes in

Goundwater

Storage

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Water Budget Data Source Types

• Basin Characterization Model (USGS)

• Napa River Streamflow (USGS)

• Updated Hydrogeologic Conceptualization and Characterization of Conditions (LSCE and MBK, 2013)

• Imported Surface Water Deliveries for All Municipalities

• Napa Sanitation District Influent Data

• US Census and California Water Plan

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Root Zone Model Napa Valley Subbasin

Precipitation

Irrigation

(applied water)

Groundwater

Recharge

Runoff

Transpiration

Evapotranspiration (ET)

Evaporation

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Root Zone Model

Evapotranspiration

Groundwater

Recharge

Precipitation

Irrigation

Wilting Point

Field Capacity

Available Water Capacity

Soil

Moisture

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Model calculates root zone water balance on monthly time steps

over a 28-year period.

Root Zone Model – Irrigated Land

0

5

-5

0

5

10

15

2009-Oct 2009-Dec 2010-Feb 2010-Apr 2010-Jun 2010-Aug

0

5Potential ET = Actual ET

0

5

10

15

Precipitation

Evapotranspiration

End of Month Soil Moisture

Groundwater Recharge

Groundwater Pumping

Soil Moisture Irrigation

inches

inches

inches

inches

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Root Zone Model – Non-Irrigated Land

0

5

0

2

4

6

8

10

12

2009-Oct 2009-Dec 2010-Feb 2010-Apr 2010-Jun 2010-Aug

0

5

10

0

5

10

15

Precipitation

Evapotranspiration

End of Month Soil Moisture

Groundwater

Recharge

Soil Moisture

inches

inches

inches

inches

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Actual ET

Potential ET

RZM Land Use and Soils Inputs

Land Use Category

Water Source

Irrigation Status

Root Depth

Available Water

Capacity

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RZM Monthly Hydrologic Inputs

are interpolated to

more than 16,000 land units

for which GW recharge and

water use for irrigation is individually calculated.

Results are aggregated to Subbasin-wide totals

in monthly time steps for 28 years.

Monthly precipitation grids

and

monthly reference ET grids

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Future Scenario

• Future climate simulated from 2016 – 2025 based on downscaled climate model outputs for Napa Valley

• Future land uses held constant at 2011 land use mapping, based on the limited number of pending discretionary projects in the Subbasin (Valley Floor).

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Root Zone Model Output

0

10

20

30

40

50

60

-40,000

-20,000

0

20,000

40,000

60,000

80,000

100,000

120,000

140,000

160,000

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88

19

89

19

90

19

91

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92

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93

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94

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95

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96

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97

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99

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00

20

01

20

02

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03

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04

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05

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Pre

cip

itatio

n [in

ches]

acre

-feet

Water Year

GW Recharge[ac-ft]

Net GW Storage Changefrom Root Zone Processes [ac-ft]

Total GW Pumpingfor Irrigation [ac-ft]

Total AnnualPrecipitation[in]

Future

Scenario

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Groundwater Pumping

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Groundwater Use 2012 – 2015 Average Acre-Ft/Yr

Vineyard Irrigation 12,651

Other Ag Irrigation 522

Unincorporated Residential (indoor and outdoor irrigation)

1,100

Semi-Ag, Residential, and Commercial Unincorporated Areas, Irrigation

4,393

Unincorporated Wineries 1,222

Municipal 295

Total GW Pumping 20,184

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Water Budget In Balance

Inflows

Upland Runoff

Uplands Subsurface Inflow

Imported SW Deliveries

GW Recharge

Outflows

Total GW Pumping

Urban Waste- water Outflow

SW Outflow and Baseflow

GW Subsurface Outflow

≈

Inflows and outflows should balance over long-term.

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DRAFT Water Budget Results

Est. Inflows

Avg. Annual Acre-Ft/Yr

Upland Runoff 148,000

GW Recharge 67,000

Imported SW Deliveries

15,000

Uplands Subsurface Inflow

6,000

Est. Outflows

Avg. Annual Acre-Ft/Yr

SW Outflow and Baseflow

178,000

Total GW Pumping

15,000

GW Subsurface Outflow

19,000

Urban Waste- water Outflow

8,000

=

Net Avg. Annual Change in Subbasin Storage = 17,000 Acre-Ft/Yr (uncertainty in individual budget components)

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Change in Groundwater Storage

Mapped Alluvium Isopach Contours and Geologic Cross

Sections (3-D view) (LSCE and MBK, 2013)

First Step: Define 3-D boundary of Alluvium

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Change in Groundwater Storage

Interpolated Depth to Base of Alluvium

Interpolated Spring Groundwater Levels

for 28 years

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Change in Groundwater Storage

• 3D GIS Models of

Saturated Aquifer Volumes (V)

are generated for 28 Years

• Change in Groundwater Storage =

Change in Aquifer Volumes (ΔV) Between 2 yrs x Specific Yield

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V1 V2

ΔV=V2-V1

Change in Groundwater Storage

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0

5

10

15

20

25

30

35

40

45

50

-30,000

-25,000

-20,000

-15,000

-10,000

-5,000

0

5,000

10,000

15,000

20,000

25,000

30,000

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Pre

cip

itatio

n (

inches)

Change in S

tora

ge (

acre

-feet)

Year

Change in GW Storage from Previous Year (acre-feet) Napa State Hospital Annual Precip Totals (inches)

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Sustainable Yield

• Sustainable yield is not a fixed value for a given basin or subbasin.

• Chapter 6 draft references recent groundwater pumping rates to estimate a base period sustainable yield.

• The calculated positive average storage change indicates the influence of uncertainties.

• Refinements to the analyses will be conducted in response to comments prior to finalization.

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CHAPTER 7: Napa Valley Subbasin Sustainability Goal

SGMA requires each agency to establish a sustainability goal for the basin (Section 354.24)

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Sustainability Goal

• Napa Valley Subbasin SGMA Sustainability Goal*: To protect and enhance groundwater quantity and quality for all the people who live and work in Napa County, regardless of the source of their water supply. The County and everyone living and working in the county will integrate stewardship principles and measures in groundwater development, use, and management to protect economic, environmental, and social benefits and maintain groundwater sustainability indefinitely without causing undesirable results, including unacceptable economic, environmental, or social consequences.

* Expanded based on GRAC sustainability goal (GRAC goal in yellow text; white text to meet SGMA intent).

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Sustainable Yield and Related Terms

Sustainable Yield (Definition; Water Code Section

10721(v)):

“Maximum quantity of water, calculated over a

base period representative of long-term conditions

in the basin and including any temporary surplus,

that can be withdrawn annually without causing an

undesirable result.”

“Undesirable Result” – key term linked to

accomplishing sustainability.

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Groundwater Sustainability

Lowering of GW Levels

Reduction of GW Storage

Seawater Intrusion

Water Quality Degradation

Land Subsidence

Depletion of Surface Water

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Representative Monitoring Sites

• Representative wells to ensure sustainability

• 18 locations

• Metrics for each sustainability indicator, as applicable

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Minimum Thresholds and Measurable Objectives

• Minimum Threshold (MT) “a numeric value for each sustainability indicator used to define undesirable results” (Section 351) • Measurable Objective (MO) “specific, quantifiable goals for the maintenance or improvement of specified groundwater conditions” (Section 351)

MO

MT

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(DWR, March 2016)

Napa River System: Most Sensitive Sustainability Indicator

• Napa River system is the most sensitive sustainability indicator in the Napa Valley Subbasin – Measurable objectives and minimum thresholds are

recommended to ensure GW sustainability or improve GW conditions

• Napa Valley Subbasin has been sustainably operated for more than 10 years; overall GW conditions stable. Baseflow is lower and/or not present at some locations during the summer to fall period, pending the water year type (Grossinger, 2012; Faye, 1973).

• SGMA: GSP/alternative submittal not required to address undesirable results that occurred before and have not been corrected by, January 1, 2015. GSA/local agency has discretion to set measurable objectives and timeframes for achieving them.

(Section 10727.2).

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Representative Monitoring Sites

• 9Q2: location of representative well for example (next slide)

9Q2

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Relationship Between Fall Groundwater Levels and Baseflow

Minimum Threshold

(127 ft; min. Fall GWE)

Measurable Objective

(135 ft; mean Fall GWE)

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Groundwater Elevations to Avoid Streamflow Depletion Serve as Proxies for Other Indicators

• The streamflow minimum thresholds represent the lowest GW elevation (GWE) that has occurred historically in the fall; below this GWE, additional streamflow depletion is likely to occur.

• These levels are not acceptable on a continuous basis as this would contribute to a worsening of existing conditions.

• These minimum thresholds also serve as proxies for other sustainability indicators.

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Next Steps

• Complete draft Basin Analysis Report

• Public Workshop: November 3, 2016

• Respond to comments

• Prepare final draft Basin Analysis Report

• Napa County Board of Supervisors: December 6, 2016

• Submit Basin Analysis Report to DWR before January 1, 2017

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Thank You 51